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319d91ee72
The extent_map structure is very critical to btrfs, as it is involved for both read and write paths. Unfortunately the structure is not properly explained, making it pretty hard to understand nor to do further improvement. This patch adds extra comments explaining the major members based on my code reading. Hopefully we can find more members to cleanup in the future. Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
199 lines
5.6 KiB
C
199 lines
5.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef BTRFS_EXTENT_MAP_H
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#define BTRFS_EXTENT_MAP_H
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#include <linux/compiler_types.h>
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#include <linux/rwlock_types.h>
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#include <linux/rbtree.h>
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#include <linux/list.h>
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#include <linux/refcount.h>
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#include "misc.h"
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#include "extent_map.h"
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#include "compression.h"
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struct btrfs_inode;
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struct btrfs_fs_info;
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#define EXTENT_MAP_LAST_BYTE ((u64)-4)
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#define EXTENT_MAP_HOLE ((u64)-3)
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#define EXTENT_MAP_INLINE ((u64)-2)
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/* bits for the extent_map::flags field */
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enum {
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/* this entry not yet on disk, don't free it */
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ENUM_BIT(EXTENT_FLAG_PINNED),
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ENUM_BIT(EXTENT_FLAG_COMPRESS_ZLIB),
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ENUM_BIT(EXTENT_FLAG_COMPRESS_LZO),
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ENUM_BIT(EXTENT_FLAG_COMPRESS_ZSTD),
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/* pre-allocated extent */
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ENUM_BIT(EXTENT_FLAG_PREALLOC),
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/* Logging this extent */
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ENUM_BIT(EXTENT_FLAG_LOGGING),
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/* This em is merged from two or more physically adjacent ems */
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ENUM_BIT(EXTENT_FLAG_MERGED),
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};
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/*
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* This structure represents file extents and holes.
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*
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* Unlike on-disk file extent items, extent maps can be merged to save memory.
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* This means members only match file extent items before any merging.
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*
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* Keep this structure as compact as possible, as we can have really large
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* amounts of allocated extent maps at any time.
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*/
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struct extent_map {
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struct rb_node rb_node;
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/* All of these are in bytes. */
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/* File offset matching the offset of a BTRFS_EXTENT_ITEM_KEY key. */
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u64 start;
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/*
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* Length of the file extent.
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*
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* For non-inlined file extents it's btrfs_file_extent_item::num_bytes.
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* For inline extents it's sectorsize, since inline data starts at
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* offsetof(struct btrfs_file_extent_item, disk_bytenr) thus
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* btrfs_file_extent_item::num_bytes is not valid.
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*/
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u64 len;
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/*
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* The file offset of the original file extent before splitting.
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*
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* This is an in-memory only member, matching
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* extent_map::start - btrfs_file_extent_item::offset for
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* regular/preallocated extents. EXTENT_MAP_HOLE otherwise.
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*/
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u64 orig_start;
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/*
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* The full on-disk extent length, matching
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* btrfs_file_extent_item::disk_num_bytes.
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*/
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u64 orig_block_len;
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/*
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* The decompressed size of the whole on-disk extent, matching
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* btrfs_file_extent_item::ram_bytes.
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*/
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u64 ram_bytes;
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/*
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* The on-disk logical bytenr for the file extent.
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*
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* For compressed extents it matches btrfs_file_extent_item::disk_bytenr.
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* For uncompressed extents it matches
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* btrfs_file_extent_item::disk_bytenr + btrfs_file_extent_item::offset
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*
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* For holes it is EXTENT_MAP_HOLE and for inline extents it is
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* EXTENT_MAP_INLINE.
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*/
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u64 block_start;
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/*
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* The on-disk length for the file extent.
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*
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* For compressed extents it matches btrfs_file_extent_item::disk_num_bytes.
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* For uncompressed extents it matches extent_map::len.
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* For holes and inline extents it's -1 and shouldn't be used.
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*/
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u64 block_len;
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/*
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* Generation of the extent map, for merged em it's the highest
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* generation of all merged ems.
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* For non-merged extents, it's from btrfs_file_extent_item::generation.
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*/
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u64 generation;
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u32 flags;
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refcount_t refs;
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struct list_head list;
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};
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struct extent_map_tree {
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struct rb_root_cached map;
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struct list_head modified_extents;
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rwlock_t lock;
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};
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struct btrfs_inode;
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static inline void extent_map_set_compression(struct extent_map *em,
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enum btrfs_compression_type type)
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{
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if (type == BTRFS_COMPRESS_ZLIB)
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em->flags |= EXTENT_FLAG_COMPRESS_ZLIB;
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else if (type == BTRFS_COMPRESS_LZO)
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em->flags |= EXTENT_FLAG_COMPRESS_LZO;
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else if (type == BTRFS_COMPRESS_ZSTD)
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em->flags |= EXTENT_FLAG_COMPRESS_ZSTD;
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}
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static inline enum btrfs_compression_type extent_map_compression(const struct extent_map *em)
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{
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if (em->flags & EXTENT_FLAG_COMPRESS_ZLIB)
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return BTRFS_COMPRESS_ZLIB;
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if (em->flags & EXTENT_FLAG_COMPRESS_LZO)
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return BTRFS_COMPRESS_LZO;
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if (em->flags & EXTENT_FLAG_COMPRESS_ZSTD)
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return BTRFS_COMPRESS_ZSTD;
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return BTRFS_COMPRESS_NONE;
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}
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/*
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* More efficient way to determine if extent is compressed, instead of using
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* 'extent_map_compression() != BTRFS_COMPRESS_NONE'.
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*/
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static inline bool extent_map_is_compressed(const struct extent_map *em)
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{
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return (em->flags & (EXTENT_FLAG_COMPRESS_ZLIB |
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EXTENT_FLAG_COMPRESS_LZO |
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EXTENT_FLAG_COMPRESS_ZSTD)) != 0;
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}
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static inline int extent_map_in_tree(const struct extent_map *em)
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{
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return !RB_EMPTY_NODE(&em->rb_node);
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}
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static inline u64 extent_map_end(const struct extent_map *em)
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{
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if (em->start + em->len < em->start)
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return (u64)-1;
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return em->start + em->len;
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}
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void extent_map_tree_init(struct extent_map_tree *tree);
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struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
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u64 start, u64 len);
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void remove_extent_mapping(struct btrfs_inode *inode, struct extent_map *em);
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int split_extent_map(struct btrfs_inode *inode, u64 start, u64 len, u64 pre,
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u64 new_logical);
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struct extent_map *alloc_extent_map(void);
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void free_extent_map(struct extent_map *em);
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int __init extent_map_init(void);
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void __cold extent_map_exit(void);
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int unpin_extent_cache(struct btrfs_inode *inode, u64 start, u64 len, u64 gen);
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void clear_em_logging(struct btrfs_inode *inode, struct extent_map *em);
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struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
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u64 start, u64 len);
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int btrfs_add_extent_mapping(struct btrfs_inode *inode,
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struct extent_map **em_in, u64 start, u64 len);
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void btrfs_drop_extent_map_range(struct btrfs_inode *inode,
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u64 start, u64 end,
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bool skip_pinned);
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int btrfs_replace_extent_map_range(struct btrfs_inode *inode,
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struct extent_map *new_em,
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bool modified);
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long btrfs_free_extent_maps(struct btrfs_fs_info *fs_info, long nr_to_scan);
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#endif
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